1. Technical Field
The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to electrosurgical systems and methods for measuring tissue impedance through an electrosurgical cable.
2. Background of Related Art
Electrosurgery involves the application of high-frequency electric current to cut or modify biological tissue during an electrosurgical procedure. Electrosurgery is performed using an electrosurgical generator, an active electrode, and a return electrode. The electrosurgical generator (also referred to as a power supply or waveform generator) generates an alternating current (AC), which is applied to a patient's tissue through the active electrode and is returned to the electrosurgical generator through the return electrode. The alternating current typically has a frequency above 100 kilohertz (kHz) to avoid muscle and/or nerve stimulation.
During electrosurgery, the AC generated by the electrosurgical generator is conducted through tissue disposed between the active and return electrodes. The tissue's impedance converts the electrical energy (also referred to as electrosurgical energy) associated with the AC into heat, which causes the tissue temperature to rise. The electrosurgical generator controls the heating of the tissue by controlling the electric power (i.e., electrical energy per time) provided to the tissue. Although many other variables affect the total heating of the tissue, increased current density usually leads to increased heating. The electrosurgical energy is typically used for cutting, dissecting, ablating, coagulating, and/or sealing tissue.
The two basic types of electrosurgery employed are monopolar and bipolar electrosurgery. Both of these types of electrosurgery use an active electrode and a return electrode. In bipolar electrosurgery, the surgical instrument includes an active electrode and a return electrode on the same instrument or in very close proximity to one another, which cause current to flow through a small amount of tissue. In monopolar electrosurgery, the return electrode is located elsewhere on the patient's body and is typically not a part of the electrosurgical instrument itself. In monopolar electrosurgery, the return electrode is part of a device typically referred to as a return pad.
Electrosurgical generators make use of voltage and current sensors to measure quantities, such as power and tissue impedance, for controlling the output of the electrosurgical generator to achieve a desired clinical effect. The voltage and current sensors are often located inside the electrosurgical generators to save costs associated with incorporating sensors into the surgical instruments. A cable, which may be more than a meter in length, connects the electrosurgical generator to the active and return electrodes and is used to deliver electrosurgical energy to tissue being treated.
The cable creates a circuit network between the voltage and current sensors and the tissue being treated, which results in inaccurate power and impedance measurements. Thus, to more accurately measure power and impedance, many generators employ compensation algorithms that account for the impedance of the cable's circuit network. These compensation algorithms typically involve solving Kirchhoff current and voltage equations for multiple nodes in a circuit model that models the cable's circuit network. However, solutions to these equations, when implemented by a real-time embedded software system, may require a significant amount of memory and processing power.